The role of residual monomer in PMMA powder and methods of polymerization in the finding of residual monomer in poly(methylmethacrylate) denture base.

The amount of residual monomer in methylmethacrylate resins used for denture bases is directly dependent on the polymerization procedure chosen. Residual monomer in PMMA powder has not yet been fully clarified. The aim of this study was to determine the amount of residual monomer in some PMMA powders used for denture bases. The study included determination of the amount of residual monomer in specimens polymerized by various methods of polymerization, attempting to test the interrelationship between the finding of residual monomer in PMMA powder and the respective group of heath-cured resin specimens. Materials from the group of poly(methylmethacrylate) resins type I, class 1 (1--Biocryl R, Galenika, Belgrade-Zemun, and 2--Major Base R, Major Dental Industry, Torino) were used in the study. Experimental specimens were divided into two groups: (1) original PMMA powders; and (2) polymerized specimens obtained by two short curing cycles (a--fractional, classical, heterogeneous polymerization; b--using the Prestherm, Bego device) and three long-curing cycles of polymerization (a--14 h at 70 degrees C; b--7 h at 70 degrees C and 3 h at 100 degrees C; and c--14 h at 70 degrees C and 3 h at 100 degrees C). By 2 g of each powder/specimen were extracted with methanol for residual monomer to be demonstrated by a modified method of gas chromatography on a device manufactured by Perkin Elmer Co. (Norwalk, Conn., USA). Original PMMA powders contained a high but varying percentage of residual monomer. Polymerized specimens had significantly lower values of residual monomer as compared to PMMA powders.(ABSTRACT TRUNCATED AT 250 WORDS)